If you mean what OS it is OSx Mountain Lion. OSx is a Unix bases graphical interface.
It depends on what you mean by "desktop". If you are referring to a "desktop computer", Apple makes two. The more popular consumer-friendly one is called the "iMac". The pricier, more professional version is called the "Mac Pro". Apple created a revolutionary new design for their Mac Pro in 2013. If you are talking about the Mac OS X interface then the desktop is actually called "The Desktop". The term refers to the base screen of the Finder, which is the program used to find and manage files on the Mac. The terms "Finder" and "Desktop" are often incorrectly used interchangeably.
The original iMac personal computer was the iMac G3. This model was released in 1998 and discontinued in 2003. One can purchase a used iMac G3 on eBay or Amazon.
The XFCE desktop interface is used with Unix and Unix compatible platforms. It is something that can be used with Solaris and Linux. It is distributed as freeware and can be downloaded from the CNET website.
It isn't very common that deals and discounts on Apple branded products are available as Apple is usually very expensive for retailers to stock. It is possible that information on discounts and specials can be found on fan websites such as Mac Rumors, and larger online stores such as Amazon may offer discount more often than most stores.
The original iMac was released in 1998. It was made by Apple Computers, and was the first computer Apple ever made which used the concept of art. It came with revolutionary USB ports and came in lots of different colours. Apple have been making iMac's ever since, with the latest one having a 27 inch Monitor.
Apple no longer produces a 20 inch iMac. You would have to buy a used one to get a 20 inch model.
I assume you're referring to the Apple logo. If so, Steve Jobs worked in a apple orchard as a kid. This is where he came up with the name Macintosh referring to the Macintosh Apple. He therefore used the Apple logo for his computers. The I in iMac stands for Internet and the Mac Stands for Macintosh.
You can get a refurbished iMac with full warranty on the Apple website for as little as $999. This is as cheap as it gets for a new iMac. Check the refurbished section and if there is none there check back each day.
If you are seeing it on the Apple website the specifications are listed there.
Probably nowhere, since it's been out of production for many years.
I believe it was there Apple II(2).
An iPhone is a certain line of smart phones shipped worldwide under the platform of Apple (maker of the iPod and iMac). The "i" used to stand for "Internet" at the time of the first iMac when Internet connection was not wireless often. It is not the vanity letter of Apple products. You can learn more about the iPhone at Apple's website. http://www.apple.com